1. Field of the Invention
The present invention relates to the field of vehicular sensor systems.
2. Discussion of Background Information
It is desirable to maintain and monitor the proper functioning of a vehicle""s brake and steering systems to enhance the safety of the driver and general public, and to help determine whether these systems meet federal safety standards for correct operation. If either the braking or steering systems of a commercial vehicle do not meet federal operational requirements, the commercial vehicle can, be placed out-of-service (xe2x80x9cOOSxe2x80x9d), until the problematic system is repaired and returned to acceptable operational limits.
Electronic parametric monitoring devices that warn of an out-of-tolerance condition to date have not been widely used and have not been generally installed by original equipment manufacturers (xe2x80x9cOEMxe2x80x9d) on new commercial vehicles. Some after-market electronic systems tend to be expensive, not readily compatible with various types of vehicles, and difficult to install.
Many of the brakes on commercial vehicles are air-powered. In a typical air-powered braking system, a brake actuator effects the movement of a pushrod, which in turn operates an S cam or disk brake mechanism, which forces the brake shoes/pads against the drums/rotors providing the friction necessary to stop the vehicle. A brake actuator may work in the following manner: upon braking compressed air fills a brake actuator chamber and a pushrod is pushed out of a brake actuator service chamber, actuating the vehicle""s braking components which are typically located in the vehicle""s brake drum. As the brake shoes/pads associated with an individual wheel wear, the pushrod must travel a greater distance in order to force the brake shoes/pads against the drums/rotors and thus provide the friction necessary to stop the vehicle. Because the pushrods have a limited length of travel, as the brake shoes/pads wear, at some point the pushrod cannot move enough to actuate the brakes fully, resulting in reduced braking force. Agencies enforcing federal and state vehicle regulations may utilize the length of pushrod travel as a measure of whether the brakes are functioning properly.
Devices known as slack adjusters are typically used to readjust the brakes as necessary to ensure that the pushrod can fully actuate the brakes. These devices are available in both automatic and manual varieties. However, if the driver fails to manually readjust the brakes regularly, or if the automatic adjuster does not function properly the brakes will eventually be in an OOS condition.
Prior art methods of monitoring braking systems can entail time-consuming and dirty work. For example, in order to determine the length of pushrod travel, one person goes under the vehicle with a measuring device (typically a ruler or tape measure) while another person applies force to the vehicle""s brake pedal in the operator""s cab. The person under the vehicle measures the distance the pushrod extends out of the brake chamber before and after brakes are applied. The difference between these two measurements is the brake stroke. This measurement is performed for each brake actuator on the vehiclexe2x80x94including any trailers attached to a semi-tractor. Although brake inspection is part of the driver""s daily vehicle inspection procedure, the inconvenience involved in monitoring braking systems results in brake stroke measurements often not be taken as often as desirable.
Some brake actuator manufacturers have addressed this problem by manufacturing systems that indicate whether brakes are operating within acceptable limits. MGM Brakes of Charlotte, N.C. manufactures one such system. MGM""s system, known as a xe2x80x9cStroke-Alertxe2x80x9d (copyright) consists of a band which is visible when the pushrod has extended to a certain length. A disadvantage of this system is that two persons are generally required to use this system; one person to press the brake pedal in the cab and one to visually inspect each brake actuator device. Other brake stroke warning devices include systems with graduated switches installed adjacent to the pushrod itself. In U.S. Pat. No. 5,450,930 to Martens et al., the switches are spaced apart so that the tripping of one switch indicates that the pushrod has started to move, and the tripping of the second switch indicates that the pushrod has moved too far. U.S. Pat. No. 5,825,287 to Zarybnicky, Sr. et al. discloses a system in which magnets are mounted on the pushrod. Switches are mounted in the housing of the brake actuator to monitor the movement of the magnets. Closure of a first switch, by passage of a first magnet over the switch, is an indication that the brake assembly is approaching a condition where maintenance may be recommended, closure of a second switch is an indication that the brakes should be immediately serviced. U.S. Pat. No. 5,433,296 to Webberley discloses a system that provides an indication to the vehicle operator of a number of different discrete positions of a brake activation arm. U.S. Pat. No. 5,825,287 to Herman discloses a method and apparatus of electronically measuring air pressure and pushrod travel and determining from those two measurements whether the brakes are properly adjusted. Pushrod travel is determined via the use of an analog oscillator circuit, whose frequency of oscillation is proportional to the distance of the brake activation arm from an electronic sensor.
In addition to proper functioning of a commercial vehicle""s braking system, it is also desirable to monitor the proper functioning of a commercial vehicle""s steering system.
Steering lash generally refers to looseness in the steering system between the steering column and steering knuckles. It is a measurement of the maximum amount of rotation the driver must exercise on a vehicle""s steering column before the vehicle""s tires begin to turn to the right or left in response to the driver""s action. Excessive steering lash results in the driver having to adjust the steering column position often and can cause excessive wear to the front tires (i.e., the steerable wheels). It can contribute to driver fatigue and impair the driver""s ability to precisely control the vehicle and can also lead to premature tire wear.
One way of measuring steering lash is to examine the amount of xe2x80x9cplayxe2x80x9d in the steering system. This measurement is made by rotating the steering column in one direction until all slack is taken up, and then rotating the steering column in the other direction until the front tires just start to move.
The invention provides methods and apparatus to measure vehicle safety parameters such as, for example, brake stroke and steering lash and describes a system which may either be easily installed in new vehicles by OEMs or in vehicles already in service.
An embodiment of the invention incorporates a brake stroke sensor that can determine the actual position of the brake pushrod at any point throughout the pushrod""s entire length of travel. The embodiment of the invention may incorporate a steering sensor, which can determine the amount of steering lash that exists in the vehicle""s steering system, and/or the amount of looseness between steerable wheels.
The present invention preferably provides a brake stroke sensor including a force-receiving plate, a second plate movable relative to the force-receiving plate, a spring disposed between the plates and operatively connected to the pushrod, a strain gauge bridge mounted on the force-receiving plate and a microcontroller for converting the strain gauge bridge signal into digital data.
The present invention also preferably provides a steering sensor including a mechanical interface operatively connected to a nonmoving member and a moving member, an encoder for transforming the rotational motion of the mechanical interface into an electrical signal, and a microcontroller capable of calculating, from the electrical signal, a count indicative of the relative positions of the members.
Various features of the invention include combined brake stroke and steering sensor with the individual and common elements of both the brake stroke and steering sensors described above; a brake stroke, steering sensor, and combined brake stroke and steering sensor utilizing a modem for transmitting data to a system controller over an electrical bus; and methods of determining brake stroke, steering lash, and steerable wheel looseness with each of the sensors herein described.